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| United States Patent |
5,096,972
|
|
Schepers
, et al.
|
March 17, 1992
|
Rubber-based graft copolymer
Abstract
The invention relates to a graft copolymer obtainable by reacting a rubbery
base polymer, which has been provided with hydroperoxide groups via
photo-oxidation, with one or more radical-polymerizable graft monomers,
the graft copolymer being based upon 90-20 parts of a rubbery base polymer
containing at least 4 (four) hydroperoxide groups per rubber chain and
80-10 parts of one or more of the graft monomers.
| Inventors:
|
Schepers; Herman A. J. (Stein, NL);
Seevens; Rene H. M. (Geleen, NL)
|
| Assignee:
|
Stamicarbon B.V. (Geleen, NL)
|
| Appl. No.:
|
430262 |
| Filed:
|
November 2, 1989 |
Foreign Application Priority Data
| Current U.S. Class: |
525/309; 525/308; 525/310; 525/316; 525/319 |
| Intern'l Class: |
C08F 255/06; C08F 279/02; C08F 253/00; C08F 279/04 |
| Field of Search: |
525/308,309,310,316,319
|
References Cited
U.S. Patent Documents
| 2911398 | Nov., 1959 | Vandenberg.
| |
| 2972605 | Feb., 1961 | Natta et al.
| |
| 3484353 | Dec., 1969 | Sharp | 525/388.
|
| 3489822 | Jan., 1970 | Witt et al.
| |
| 3846266 | Nov., 1974 | Duynatee | 525/388.
|
| 4166081 | Aug., 1979 | Fournier | 525/86.
|
| 4704431 | Nov., 1987 | Stuart | 525/86.
|
| 4716197 | Dec., 1987 | Seiss | 525/86.
|
| 4788250 | Nov., 1988 | Kitahara | 525/86.
|
| Foreign Patent Documents |
| 8606731 | Nov., 1986 | WO.
| |
Other References
European Search Report and Annex, Application No. 89202755.8.
|
Primary Examiner: Marquis; Melvyn I.
Assistant Examiner: Jagannathen; Vasu S.
Attorney, Agent or Firm: Cushman, Darby and Cushman
Claims
We claim:
1. Graft copolymer obtainable by reacting:
A) a rubbery base polymer that has been provided with hydroperoxide groups
via photo-oxidation, with
B) one or more radical-polymerizable graft monomers, characterized in that
the graft copolymer is based upon
a) 90-20 parts by weight of a rubbery base polymer containing at least 4
(four) hydroperoxide groups pr rubber chain wherein said rubbery based
polymer is selected from the group consisting of olefinically unsaturated
polymers and ethylene-60 -alkene-diene-polymers, and
b) 80-10 parts by weight of one or more of the graft monomers.
2. Graft copolymer according to claim 1, characterized in that the rubber
base polymer contains 5-35 hydroperoxide groups per rubber chain.
3. Graft copolymer according to claim 1, characterized in that the rubbery
base polymer contains 6-20 hydroperoxide groups per rubber chain.
4. Graft copolymer according to claim 1, characterized in that the graft
copolymer consists of the reactionproduct of
a) 75-50 parts by weight of A), with
b) 50-25 parts by weight of B).
5. Graft copolymer according to claim 1, characterized in that B) is a
monovinyl-aromatic monomer, whether or not substituted.
6. Graft copolymer according to claim 5, characterized in that B) is a
combination of a) a monovinyl-aromatic monomer, whether or not
substituted, and b') an unsaturated nitrile monomer or b") an .alpha.- or
.beta.-unsaturated carboxylic acid or a derivative thereof.
7. Graft copolymer according to claim 6, characterized in that b') is
acrylonitrile.
8. Graft copolymer according to claim 1, characterized in that B) is methyl
methacrylate.
9. Graft copolymer according to claim 1, characterized in that the
spirit-extractable fraction has been removed from the product of the
grafting reaction.
10. Process for the preparation of a graft coolymer by reacting:
A) a rubbery base polymer that has been provided with hydroperoxide groups
via photo-oxidation, with
B) one or more radical-polymerizable graft monomers, characterized in that
(a) 90-20 parts by weight of a rubbery based polymer containing at least 4
(four) hydroperoxide groups per rubber chain are reacted with
(b) 80-10 parts by weight of one or more of the graft monomers at a
temperature of between 20.degree. and 150.degree. C.,
wherein said rubbery based polymer is selected from the group consisting of
olefinically unsaturated polymers and
ethylene-.alpha.-alkene-diene-polymers.
Description
The invention relates to a graft copolymer obtainable by reacting A) a
rubbery base polymer that has been provided with hydroperoxide groups via
photo-oxidation, with B) one or more radicalpolymerizable graft monomers.
Such a graft copolymer is known from W086/06731. In this publication such a
graft copolymer is used in a melt blend with a rigid matrix based on a
monovinyl-aromatic monomer. In the preparation of the graft copolymer a
rubbery base polymer, provided with hydroperoxide groups via
photo-oxidation, is used as starting product.
The general process of grafting one or more radicalpolymerizable monomers
onto a rubbery base polymer provided with hydroperoxide groups has been
known for a long time. Rubbery base polymers can be provided with
hydroperoxide groups by means of oxidation reactions with the aid of
per-compounds, such as persulphates and peroxides, or by means of
autocatalytic oxidation reactions. However, both types of reactions
results in polymer derivatives which, in addition to a small number of
hydroperoxide groups, contain a large variety of other oxygen-containing
groups, such as hydroxyl, ketone, aldehyde, carboxyl and ester groups. Not
only is the yield of hydroperoxide groups small with such processes and
are groups formed in an onto the polymer chains which are not always
harmless to the properties of the polymer prepared, but these processes
also lead to a certain degree of chain scission, which results in a large
number of different compounds and simultaneous crosslinking. These
compounds can have an adverse effect on the properties of the polymer
derivatives thus obtained. Examples of such polymer derivatives are to be
found in US-A-3,489,822.
The American patent U.S. Pat. No. 3,484,353 suggests a process for the
preparation of hydroperoxide derivatives of polymers which contain
intralinear C.dbd.C unsaturations in the chain, which process consists in
subjecting such polymers to irradiation with visible light in the presence
of oxygen and a photosensitizer (photo-oxidation).
In U.S. Pat. No. 3,846,266 a hydroperoxide derivative is prepared, also by
photo-oxidation of a rubbery base polymer, by using polymers containing
C.dbd.C bonds in the non-linear part of the polymer chain, the carbon
atoms of which possess either two hydrocarbon groups in vicinal cis
position with respect to one another which do not form part of the same
cyclic structure or at least three hydrocarbon groups.
In the aforementioned WO86/06731 the graft copolymer is prepared by
photo-oxidizing the rubber dissolved in the graft monomer or graft
monomers in such a manner that 0.5-4 hydroperoxide groups are formed per
rubber chain, after which the polymerization is carried out. This does not
only result in graft copolymerization of the monomer or the monomers onto
the rubber chain, but also in--substantial--polymerization of the monomer
or the monomers, which in its entirety leads to a rubber-modified styrene
polymer.
The applicant has found that when a different graft base is chosen, the
graft copolymer according to the invention also presents improved
properties as compared with the already known graft copolymers, such as
greater strength, provided that a specified weight ratio between the graft
base and the graft monomers is adhered to.
The graft copolymer according to the application is thus characterized in
that it is based upon a) 90-20 parts by weight of a rubbery base polymer
containing at least 4 (four) hydroperoxide groups per rubber chain, and b)
80-10 parts by weight of one or more of the graft monomers.
Surprisingly, by using a rubbery base polymer with more than 4
hydroperoxide groups per rubber chain, a graft copolymer is obtained which
has greatly improved properties compared with the known graft copolymers
as described in WO 86/06731, which states that optimum properties are
obtained in the range of 0.5-4 hydroperoxide groups per rubber chain. The
number of hydroperoxide groups per rubber chain is obtained by multiplying
the number of hydroperoxide groups per kilogram of rubbery base polymer by
the number average molar mass of the rubbery base polymer, expressed in
kilograms per mole.
It seems likely that such improved properties are the result of the fact
that improved grafting onto the rubber chain is obtained by using at least
4 hydroperoxide groups per rubber chain. The applicant has found that the
conversion of hydroperoxide groups into graft copolymer is far from
effective. Only a limited number of hydroperoxide groups is converted into
graft copolymer chains of sufficient length.
For the sake of simplicity and clarity the constituent parts of the graft
copolymer will be discussed separately below.
A) The rubbery base polymer
As graft base of the present application use may be made of rubbery base
polymers which can be provided with hydroperoxide groups via
photo-oxidation. The polymers described in U.S. Pat. No. 3,484,353 and
those in U.S. Pat. No. 3,846,266 as well as mixtures hereof may be used.
Examples hereof are:
olefinically unsaturated polymers such as:
natural rubbers;
polymers derived from diolefin, such as butadiene, chloroprene,
copolymers derived from diolefin and vinyl compounds, such as styrene,
acrylonitrile,
ethylene-.alpha.-alkene-diene-polymers (EADM rubbers), which polymers must
meet the criteria given in U.S. Pat. No. 3,846,266.
All these rubbery base polymers may be provided with hydroperoxide groups
via the photo-oxidation process known per se; see the aforementioned U.S.
patents.
Photo-oxidation is here understood to be an oxidation in which light and a
photo-sensitizer convert oxygen into singlet oxygen, which singlet oxygen
then effects the oxidation of the polymer. For the sake of clarity it
should be mentioned here that this concept does not include auto-oxidation
catalyzed by light. Photo-oxidation reactions can be distinguished from
auto-oxidation reactions by the addition of oxidation inhibitors.
Oxidation inhibitors slow down auto-oxidations but not photo-oxidations.
The light to be used may vary considerably in wavelength. Visible light is
preferred. The light used may both monochromatic and polychromatic. The
effectiveness of the light used depends greatly on the choice of the
sensitizer used. The light used must be sufficiently absorbed by the
sensitizer to render good effectiveness. Light with a wavelength differing
from that of visible light results in a certain degree of photo-oxidation
with the formation of hydroperoxide groups in the polymer but also leads
to auto-oxidation, photolysis and other radical reactions, which, in turn,
can lead to the formation of undesired products.
The photo-oxidation can be effected at almost any temperature, since the
rate of photo-oxidation reactions is virtually independent of the
temperature. The only temperatures that must be avoided are those at which
the hydroperoxide groups formed immediately decompose again. On the whole,
a temperature may be used between -50.degree. C. and +120.degree. C., and
more in particular between 0.degree. C. and 100.degree. C.
The photo-oxidation can be effected using polymers in solution, in
dispersion or in latex, or solid polymers.
If use is made of a polymer in solution the choice of the solvent is
greatly dependent on the solubility of the contained rubbery polymer. In
general, use may be made of hydrocarbons, for example alkanes such as
n-pentane, n-hexane, isooctane, n-octane, nonane, decane, aromatics such
as toluene or xylene. Other solvents such as pyridine, tetrahydrofuran,
acetone, alcohols such as methanol and ethanol and dimethyl sulphoxide may
also be used.
The photo-oxidation can also be carried out if the polymer is a solid, a
photo-sensitizer also being incorporated in the solid phase. It is for
example possible to use a polymer in the form of crumb or moulded products
(such as sheets).
The oxygen concentration is preferably chosen sufficiently high so that it
does not determine the speed of the photo-oxidation. To this effect it is,
for example, possible to supply oxygen at a speed that is at least the
same as the speed at which oxygen is absorbed into the polymer. Any method
that is suitable for mixing a gas and a (viscous) liquid or solid may be
used.
As oxygen source use may be made of both pure oxygen and an oxygen mixture,
diluted with inert gases, such as nitrogen. Air is very suitable for this
purpose.
Any photo-sensitizer may be used. The effectiveness of these
photo-sensitizers may vary considerably and depends greatly on the
wavelength of the light used. Examples of suitable photo-sensitizers are
porphin derivatives such as tetraphenyl porphin, and further for instance
chlorophyll, casein, methylene blue, methyl violet, fluorescein, hemin,
anthracene, acridine and Rose Bengal.
The amount of sensitizer may vary within wide limits, but usually only
small amounts are used, for example between 0.001 and 0.1 wt. % relative
to the weight of the polymer used.
The concentration of hydroperoxide groups on the photo-oxidized rubbery
base polymer can be calculated by reducing the hydroperoxide groups with
triphenylphosphine. The concentration of hydroperoxide groups per kilogram
of rubber can be determined from the amount of triphenylphosphine oxide
formed, which can be analysed by means of gas chromatography. Another very
suitable method for determining the amount of hydroperoxide groups is the
following: photo-oxidation tests with a model substance
(2-ethylidene-norbornane) have shown that the oxygen absorbed in the
photo-oxidation is, in molar terms, quantitatively converted into
hydroperoxide; in addition, that reducing this with an excess of
triphenylphosphine results in complete conversion into hydroxylnorbornane.
It has also been found that (in molar terms) the maximum amount of oxygen
absorbed corresponds to the concentration of photo-oxidizable compound(s)
in both the model substance and the rubbery polymer. The absorbance at two
wavelengths relevant to hydroxyl (3600 and 3400 cm-1) of photo-oxidized
rubber that has been converted into the corresponding hydroxyl rubber by
treatment with triphenylphosphine can be determined via infrared
transmission spectrophotoscopy. By preparing mixtures of known
photo-oxidized (and then reduced) rubbers on the one hand and, on the
other, the starting materials, two calibration lines are obtained per
rubber starting material. With the aid of these calibration lines, the
concentration of hydroperoxide groups in any photo-oxidized rubbery base
polymer can be determined, after reduction with triphenylphosphine.
The number of hydroperoxide groups per rubber chain is calculated by
multiplication with the number-average molar weight of the rubbery base
polymer used (which can be determined with the aid of, for example, gel
permeation chromatography).
It is advantageous to use a rubbery base polymer with 5-35 hydroperoxide
groups per chain, in particular with 6-20 hydroperoxide groups per chain.
The maximum possible number of hydroperoxide groups per rubber chain is,
of course, determined by the concentration of photo-oxidizable groups in
the rubbery base polymer. On the basis of the results obtainable with the
graft copolymer, a person skilled in the art can easily determine,
starting from the doctrine of the present application, how many
photo-oxidizable groups the rubbery base polymer must have.
(B) Graftable, radical-polymerizable monomers
Any monomer or combination of monomers that can be polymerized via a
radical mechanism may be used as basic grafting material for the graft
copolymer.
For example, monovinyl-aromatic monomers are very suitable for use as a
graft copolymer according to the invention. Examples of this are:
styrene, whether or not substituted (such as styrene, .alpha.-alkyl
styrenes, halo-substituted styrenes, ring-substituted alkyl styrenes),
vinylnaphthalene,
vinylanthracene.
These monomers may be used either separately or together with other
copolymerizable monomers. Examples of such copolymerizable monomers are:
unsaturated nitriles (such as acrylonitrile, methacrylonitrile)
conjugated dienes (such as butadiene)
.alpha.- or .beta.-unsaturated carboxylic acids or derivatives thereof
(anhydrides, esters or semiesters thereof, such as acrylic acid, maleic
anhydride, methyl methacrylate).
Monovinyl-aromatic monomers other than those mentioned may also be used as
basic grafting material, such as:
unsaturated nitriles (for example acrylonitrile)
.alpha.- or .beta.-unsaturated carboxylic acids or derivatives thereof
(anhydrides, esters or semiesters, such as acrylic acid, maleic anhydride,
methyl methacrylate).
vinyl halides (such as vinyl chloride).
(C) The graft copolymer
The graft copolymer according to the invention can be prepared by grafting
one or more radical-polymerizable monomers onto the rubbery base polymer
provided with hydroperoxide groups. A copolymer that has been subjected to
the grafting reaction for a sufficiently long time so that the
hydroperoxide groups have been largely converted during the grafting, is
particularly preferred. This can be determined or derived in various
manners:
a) by determining the residual hydroperoxide content via reduction with
triphenylphosphine (similarly to the determination of the original content
of hydroperoxide groups).
b) the concentration of residual hydroperoxide groups can, for example, be
derived from:
1) the change in the concentration of the product that is soluble in spirit
during the grafting or
2) the change in the concentration of graft monomer(s) of the graft
copolymer as a function of the grafting time.
If the hydroperoxide groups have been completely converted the
concentration of product that is soluble in spirit or the concentration of
graft monomer(s) of the graft copolymer will remain constant with time.
The graft copolymerization can be carried out in various manners.
Preferably a solution of the rubbery base polymer provided with
hydroperoxide groups is subjected to the action of the monomer (or
monomers) desired. Any conventional, inert solvent for the polymer may be
used. The solvent may be aliphatic, cycloaliphatic or aromatic, whether or
not substituted. Examples are (cyclo)hexane, xylene, chlorobenzene and
toluene.
If a solvent for the rubbery base polymer has been used in the preparation
of the hydroperoxide, it is preferable to also use that solvent in the
grafting-process.
The grafting temperature may be room temperature, but more commonly
elevated temperatures are used (over 50.degree. C.), but preferably not
over 150.degree. C., because then the thermal polymerization into homo- or
copolymers will gain the upper hand.
The reaction product obtained can be isolated by methods known per se, such
as evaporation, steam distillation or via e.g. precipitation. The homo- or
copolymer that is also formed from the monomers used in the
grafting-process can be separated from the graft copolymer via extraction
with a suitable solvent, such as acetone or MEK (methyl ethyl ketone). The
choice of solvent is subject to the condition that the homo-/copolymer
formed shall dissolve and the graft copolymer shall not.
As component B) use is advantageously made of a monovinylaromatic monomer,
whether or not substituted. Examples are: styrene, .alpha.-methylstyrene,
para-methylstyrene, halogenated styrenes. More in particular such a
monomer is used in combination with either b') an unsaturated nitrile
monomer (preferably acrylonitrile) or b") an .alpha.or .beta.unsaturated
carboxylic acid or a derivative thereof (preferably methyl methacrylate or
maleic anhydride).
It is also a advantage to use methyl methacrylate as graft monomer.
A special feature of such available graft copolymers is that they have good
resistance to organic solvents; they have increased rigidity and strength.
The graft copolymer according to the invention is eminently suitable for
use as a thermoplastic elastomer if the graft copolymer consists of the
reactionproduct of:
a) 75-50 parts by weight of A), with
b) 50-25 parts by weight of B)
A particularly good product is obtained when the fraction that is
extractable with spirit is removed from the graft copolymer thus obtained.
This improves the aforementioned and other properties of the graft
copolymer even more compared with those of the original graft copolymer.
Graft copolymers according to the invention may be used as such, but may
also be vulcanized first with the aid of conventional vulcanizing agents.
The graft copolymers according to the invention may also contain the usual
additives such as antistats, antioxidants, lubricants, flame retardants,
stabilizers, pigments, chalk, etc.
The invention will be further elucidated with the aid of the following
examples, without being limited hereto.
EXAMPLE I
A 150-Watt halogen lamp had been placed beneath a glass reaction vessel
with a volume of 4.0 l and a flat bottom. The reaction vessel was equipped
with a heating jacket, an inlet tube, a thermometer, a stirrer and a
cooler with a discharge tube.
Into the reactor 1.60 l of xylene was introduced in which 0.227 kg of
KELTAN 312.sup.R [EPDM rubber of DSM] and 1.14 g of Irganox 1076.sup.R
[stabilizer of Ciba Geigy] had been dissolved. In addition to 54% (m/m) of
ethylene, the rubber contained 4.4% (m/m) of 2-ethylidene-norbornene. Its
Mooney viscosity was 36 (ML 1+4, 125.degree. C.). The
ethylidene-norbornene group of the rubber is photo-oxidized.
With stirring, and at a temperature of 80.degree. C., the liquid was
saturated with pure oxygen supplied via the inlet tube.
After the addition of 10.5 mg of tetraphenylporphine as sensitizer, a gas
burette filled with oxygen was connected to the reactor, which was then
illuminated. After 5.25 hours the oxygen absorbance was no longer
measurable. The amount of oxygen absorbed was 1.876 l NTP (=0.0837 moles).
The amount of KELTAN 312 used contained 0.0832 moles of
2-ethylidene-norbornene as measured with the aid of pyrolysis gas
chromatography, after calibration with model substances. After the
aforementioned photo-oxidation the absorbance of the
2-ethylidene-norbornene group at 1690 cm.sup.-1 that is relevant for
infrared transmission spectrophotoscopy (Perkin Elmer 682) appeared to be
no longer measurable. Comparable tests with the model substance
2-ethylidene norbornene also showed that in molar terms the amount of
oxygen absorbed corresponded to the conversion into hydroperoxide, as
determined by titration with potassium iodide.
A small sample of the reaction liquid was reduced with an excess of
triphenylphosphine and the hydroxyl-containing rubber thus obtained was
recovered by precipitation in acetone and drying. The Hoekstra plasticity
of the sample was determined. This appeared to have hardly changed (KELTAN
312 blank: 40; after photo-oxidation: 42). No gel had been formed either
(boiling toluene, 20 hours). Infrared transmission spectrophotoscopy
showed that the rubber had not oxidized. Apparently the molecular
structure of the rubber had hardly changed.
In addition, the absorbances relevant for hydroxyl were measured at 3600
and 3400 cm.sup.-1 and standardized at 10 mg/cm.sup.2. For the absolute
analysis of random samples, of importance for the following examples, the
aforementioned absorbances were measured of ten different mixtures (with
known compositions) of the KELTAN 312 starting product and the
hydroxyl-containing KELTAN 312 described above, and calibration lines were
drawn.
A calibrated gel permeation method (Waters M-150-C) was used to determine
the number average molar mass of the KELTAN 312 rubber used; this was
found to be 40 kg per mole. The number of hydroperoxide groups per rubber
chain of the sample described above was determined as follows (oxygen
consumption in mol/kg of rubber times the molar mass of the rubber in
kg/mole):
##EQU1##
The photo-oxidized rubber obtained was provided with polystyrene grafts by
first expelling the dissolved oxygen from the reaction mixture with the
aid of pure nitrogen, after which an extra 1.58 of xylene was added,
followed by 0.454 kg of the styrene monomer to be grafted. The grafting
was started by increasing the temperature to 120.degree. C. and was
continued for 2.5 hours.
After the grafting triphenylphosphine was added and the graft copolymer was
recovered by precipitation at room temperature, with gentle stirring in an
excess of acetone and drying.
The mass balance and the infrared transmission spectrum of the product
obtained were used to determine the styrene content of the graft
copolymer. This was found to the 33% (m/m).
The graft copolymer thus obtained was used to compression mould plates
measuring 50*50*1 mm in 3 minutes at 190.degree. C. and a pressure of 150
kN. A tensile test was carried out according to standard ISO 37 (specimen
No 3).
An extraction was carried out to determine, among other aspects, the
quality of the grafting (the portion of the original amount of rubber that
had been insufficiently grafted). To this effect the graft copolymer was
boiled in n-hexane, the principal component of (special boiling point)
spirit, for 20 hours and then centrifuged. In this manner 36% (m/m) of the
graft copolymer, based on the original amount of rubber, remained
dissolved.
Low gel content is important for good processability as a thermoplastic.
This was tested by submerging the graft copolymer contained in a CrNi wire
gauze cage with apertures of 0.3 mm in boiling toluene for 20 hours. The
residue in the case (gel) was determined by weighing after drying. The gel
content of the graft copolymer was only 14% (m/m) in spite of the high
hydroperoxide content per rubber chain of 14.8, which could potentially
cause considerable crosslinking.
The following table I gives a summary of the results obtained for the graft
copolymer.
TABLE I
__________________________________________________________________________
Example
Duration of illu-
--OOH/
Styrene
Fraction soluble
Toluene
Modulus at 100%
Tension
Elongation
No. mination hours
chain
content %
in hexane %
gel % elongation MPa
break
at break
__________________________________________________________________________
%
I 5.25 14.8 33 36 14 8.5 11.2 150
__________________________________________________________________________
The same analyses and tensile tests were used in the following examples and
comparative experiments. In addition, instead of using the gas burette
filled with oxygen, a gas mixture of 72 vol. % oxygen and 28 vol. %
nitrogen was passed through the reactor at a rate of 5 l/hour and a
pressure of 1 bar.
COMPARATIVE EXPERIMENT A
1.60 l of xylene, in which 0.227 kg of KELTAN 312 had been dissolved, was
fed to the reactor of example I. The gas mixture was passed through, with
stirring, at 90.degree. C. until the solution was saturated with oxygen.
Then 20.3 g of benzoyl peroxide (=0.084 mole) was introduced for the
formation of hydroperoxide groups on the rubber. With continued supply of
the gas mixture, the solution was left to react for 3 hours. After this,
the solution was left to postreact for another 10 minutes at 120.degree.
C. to remove the residual benzoyl peroxide.
A small sample of the reaction liquid was reduced with triphenylphosphine.
The Hoekstra plasticity appeared to have increased to 56. An infrared
transmission spectrum was recorded. The number of hydroperoxide groups per
rubber chain appeared to be 3 (as determined via the calibration lines).
The reacted rubber contained a large number of carbonyl groups, in
contrast with the photo-oxidized rubber.
The grafting was carried out according to example I. The styrene content of
the product obtained was 18% (m/m). Testing the tensile strength yielded a
modulus at 100% elongation of 1.1 MPa, a tension at break of 1.3 MPa and
an elongation at break of 310%. The hexane-soluble fraction was 95% (m/m).
No toluene gels were found.
The following table II compares the results with those of example I.
TABLE II
__________________________________________________________________________
Example No.
Duration of
Styrene
Fraction
Toluene
Modulus at
Tension
Elonga-
Comp. illumination
--OOH/
content
soluble
gel 100% elonga-
at break
tion at
exp. No
hours chain
% in hexane %
% tion MPa
MPa break %
__________________________________________________________________________
I 5.25 14.8 33 36 14 8.5 11.2 150
A n.a. 3 18 95 0 1.1 1.3 310
__________________________________________________________________________
These results show that the use of a peroxide for the formation of
hydroperoxide on a rubber leads to unsatisfactory grafting results and is
not attractive from an economic point of view.
EXAMPLES II, III and IV and COMPARATIVE EXPERIMENTS B, C and D
In these examples the influence was investigated of the number of
hydroperoxide groups per rubber chain on the composition and properties of
the graft copolymers.
The photo-oxidations were carried out according to example I. Different
amounts of hydroperoxide per rubber chain were obtained by varying the
illumination time.
The graft reactions were also carried out according to example I, with the
exception that 0.795 kg of styrene and 1.30 l of xylene were used.
TABLE III
__________________________________________________________________________
Frac-
Example
Dura- Sty-
tion Modulus
Ten-
No. tion rene
solu-
Tolu-
at 100%
sion
Elonga-
Comp.
of illu- con-
ble in
ene elonga-
at tion at
exp. mination
--OOH/
tent
hexane
gel tion break
break
No. hours
chain
% % % MPa MPa %
__________________________________________________________________________
B 0 0 0*
100 0 0.6 0.6 400
C 0.17 1.1 16 81 1 0.9 1.3 300
D 0.5 2.7 27 67 1 1.8 2.3 180
II 1.0 4.3 34 54 1 5.2 6.4 150
III 1.5 7.1 42 43 2 7.0 8.0 150
IV 2.5 11.5 50 33 17 17.6 18.3
130
__________________________________________________________________________
*after additional extraction with methyl ethyl ketone.
This clearly shows that a hydroperoxide content of at least four results in
a high modulus at 100% elongation and a high tension at break at a
sufficiently high elongation at break (>100%). The fraction that is
soluble in hexane has then decreased considerably.
EXAMPLES V, VI, and VII
Larger portions of the graft copolymers of examples II, III and IV were
extracted for 20 hours with boiling hexane, centrifuged and dried. Tensile
testing of compression moulded plates manufactured from the graft
copolymers thus obtained shows the following results (Table IV).
TABLE IV
______________________________________
Sty- Fraction
Modulus Elon-
rene soluble
at 100%
Tension
ga-
Ex- con- in elonga-
at tion at
ample --OOH/ tent hexane tion break break
No. chain % % MPa MPa %
______________________________________
II 4.3 34 54 5.2 6.4 150
V 4.3 50 0 12.6 18.1 160
III 7.1 42 43 7.0 8.0 150
VI 7.1 53 0 16.3 18.6 140
IV 11.5 50 33 17.6 18.3 150
VII 11.5 57 0 17.7 20.5 170
______________________________________
These examples show that removal of the hexane-soluble fraction results in
a considerable improvement of the modulus at 100% elongation and the
tension at break and hardly affects the elongation at break.
EXAMPLES VIII and IX and COMPARATIVE EXPERIMENTS E and F
These examples show the importance of the number of hydroperoxide groups
per rubber chain at (virtually) the same styrene content of the graft
copolymers.
The photo-oxidations were carried out according to examples II, III and IV
(variable illumination time).
The amounts of extra xylene and styrene used for the graftings were
necessarily adjusted (see further example I).
The following table V shows the grafting conditions and results.
TABLE V
__________________________________________________________________________
Fraction
Modulus
Ten-
Example soluble
at 100%
sion
Elonga-
No. Sty-
Styrene
in elonga-
at tion at
Comp.
--OOH/
Xylene
rene
content
hexane
tion break
break
Exp. No.
chain
l kg % % MPa MPa %
__________________________________________________________________________
E 1.3 0.6 1.37
39 63 -- 4.5 20
VIII 7.1 1.4 0.68
37 36 6.4 6.5 110
F 2.7 1.4 0.68
22 70 1.7 2.3 180
IX 15 1.8 0.30
20 48 2.1 7.5 300
__________________________________________________________________________
EXAMPLE X and COMPARATIVE EXPERIMENT G
In this example KELTAN 778.sup.R [EPDM rubber of DSM] was used as
photo-oxidizable rubber. In addition to 66% (m/m) ethylene, this rubber
contained 4.5% (m/m) 2-ethylidene-norbornene. The Mooney viscosity was 63
(ML 1+4, 125.degree. C. ). The number average molar mass was 56 kg/mole.
1.73 of xylene, 0.115 kg of rubber and 0.6 g of Irganox 1076 were used for
the photo-oxidation. The illumination time was 4 hours.
During the photo-oxidation the Hoekstra plasticity hardly changed (from 63
to 66). The number of hydroperoxide groups per rubber chain was 20, as
determined with the analytical method of example I.
An extra 1.64 l of xylene and 0.299 kg of styrene were used for the
grafting. For the rest see example I.
The following table VI gives the results.
TABLE VI
__________________________________________________________________________
Example No.
Illumina- Styrene
Fraction
Toluene
Modulus at
Tension
Elonga-
Comp. tion time
--OOH/
content
soluble
gel 100% elonga-
at break
tion at
Exp. No.
hours
chain
% in hexane %
% tion MPa
MPa break %
__________________________________________________________________________
G 0 0 0* 100 0 1.1 8.5 1100
X 4 20 34 35 18 8.1 16.4 240
__________________________________________________________________________
*after additional methyl ethyl ketone extraction.
EXAMPLES XI, XII and XIII and COMPARATIVE EXPERIMENTS H, I and J
In these examples the influence of the illumination time was investigated.
KELTAN 312 rubber was photo-oxidized in the same manner as in example II,
with an adjusted illumination time, until a hydroperoxide content per
rubber chain of 7.4 was obtained in examples XI, XII and XIII and a
hydroperoxide content per rubber chain of 1.5 in the comparative
experiments H, I and J.
The grating reactions were carried out as in example I, the only difference
being the amounts of extra xylene and styrene used. In examples XI, XII
and XIII 1.41 l of extra xylene and 0.673 kg of styrene were used. In
comparative experiments H, I and J 0.93 l of extra xylene and 1.107 kg of
styrene were used. Because of the lower hydroperoxide content in the
comparative experiments, the styrene concentration had to be higher to
obtain a somewhat comparable styrene content in the graft copolymer.
The following table VII gives the results.
TABLE VII
__________________________________________________________________________
Frac-
Example Sty-
tion
Modulus
No. rene
solu-
at 100%
Tension
Elonga-
Comp. Grafting
con-
ble in
elonga-
at tion at
Exp. --OOH/
time tent
hexane
tion break
break
No. chain
hours
% % MPa MPa %
__________________________________________________________________________
XI 7.4 1.0 18 77 2.7 4.1 180
XII 7.4 2.5 40 43 6.0 7.1 140
XIII 7.4 6.0 49 30 13.1 13.7 120
H 1.5 2.5 35 63 3.5 3.6 120
I 1.5 5.0 51 56 -- 7.9 30
J 1.5 7.0 58 52 -- 13.0 40
__________________________________________________________________________
This shows that in the case of a rubber with fewer than four hydroperoxide
groups per chain (H, I, J) the rubber character is lost (elongation<100%)
at longer grafting times. The hexane-soluble fraction then remains high.
The results of examples XI, XII and XIII show that a person skilled in the
art is able to control the properties as required also on the basis of the
grafting time.
EXAMPLES XIV and XV
In these examples two monomers, styrene and acrylonitrile were grafted onto
KELTAN 578.sup.R [EPDM rubber of DSM]. In addition to 65% (m/m) ethylene,
the rubber contained 4.3% (m/m) 2-ethylidene-norbornene. The Mooney
viscosity was 52 (ML 1+4, 125.degree. C.). The number average molar mass
was 50 kg/mole.
The photo-oxidation took place in the same manner as in example II, with
the exception that 0.100 kg of KELTAN 578 dissolved in 1.50 l of toluene
and 0.5 g of Irganox 1076 were used. The illumination time was four hours.
The number of hydroperoxide groups per rubber chain was 18, as determined
according to the method of example I.
A mixture of 0.164 kg of styrene and 0.087 kg of acrylonitrile was added
for the grafting, which was effected at 100.degree. C. for 2.5 and 4
hours, respectively. For the rest see example I.
The following table VIII shows the results.
TABLE VIII
__________________________________________________________________________
Grafting Toluene
Modulus at
Tension
Elongation
Example
time S/AN
gel 100% elonga-
at break
at break
No. hours
% % tion MPa
MPa %
__________________________________________________________________________
XIV 2.5 21 2 7.2 11.2 190
XV 4.0 29 5 16.4 16.8 110
__________________________________________________________________________
This shows the monomer mixtures can also successfully be cografted onto a
photo-oxidized rubber, resulting in a graft copolymer with good properties
.
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